Primordial Soup Was Powered By Primitive ‘Batteries’

A research team at the University of Leeds may have solved the question of how objects from space could have kindled life on Earth.

Scientists generally accept that some of the important ingredients for life came from meteorites impacting the early Earth. However, they have not been able to explain how that inanimate rock transformed into the building blocks of life.

The new study, published in Geochimica et Cosmochimica Acta, reveals how a chemical that is similar to one currently found in all living cells and is vital for generating the energy that makes something alive, could have been created when phosphorus bearing meteorites landed in hot, acidic pools of liquids around volcanoes. Such volcanoes were likely to be common across the early Earth.

“The mystery of how living organisms sprung out of lifeless rock has long puzzled scientists, but we think that the unusual phosphorus chemicals we found could be a precursor to the batteries that now power all life on Earth. But the fact that it developed simply, in conditions similar to the early Earth, suggests this could be the missing link between geology and biology,” said Dr Terry Kee, from the University’s School of Chemistry.

A process called chemiosmosis powers all life on Earth. This process breaks down the chemical adenosine triphosphate (ATP), the rechargeable chemical ‘battery’ for life, then reforms it through respiration to release energy. This energy is used to drive the reactions of life, also known as metabolism. To create and break down ATP requires complex enzymes unlikely to have been present on Earth during the period when life first developed. Knowing this led the research team to search for a more basic chemical with similar properties that does not require enzymes for energy transfer.

A key element in ATP and other fundamental building blocks of life such as DNA is phosphorus which is abundant on Earth. The most common form, phosphorus (V), is insoluble in water and has a low chemical reactivity, however. In contrast, meteorites and interstellar dust rich in exotic minerals regularly bombarded the early Earth. One of those minerals was a far more reactive version of phosphorus, the iron-nickel-phosphorus mineral schreibersite.

A simulated meteorite impact on the volcanically active early Earth was achieved by placing samples of the Sikhote-Ailin meteorite, an iron meteorite that fell in Siberia in 1947, in acid taken from the Hveradalur geothermal area in Iceland. The meteorite samples were left for four days to react with the acidic fluid in test tubes incubated by the surrounding hot spring, followed by another 30 days at room temperature.

When analyzing the resulting solution, the researchers found the compound pyrophosphite, which is a molecular “cousin” to pyrophosphate. Pyrophosphate makes up the part of ATP responsible for energy transfer. The team believes the pyrophosphite compound could have acted as an early form of ATP in what they have named “chemical life.”

“Chemical life would have been the intermediary step between inorganic rock and the very first living biological cell. You could think of chemical life as a machine — a robot, for example, is capable of moving and reacting to surroundings, but it is not alive. With the aid of these primitive batteries, chemicals became organized in such a way as to be capable of more complex behavior and would have eventually developed into the living biological structures we see today,” said Dr Terry Kee.

Recently, the mission team from NASA’s Jet Propulsion Laboratory (JPL) responsible for the Curiosity rover reported the presence of phosphorus on Mars.

“If Curiosity has found phosphorus in one of the forms we produced in Iceland, this may indicate that conditions on Mars were at one point suitable for the development of life in much the same way we now believe it developed on Earth,” added Dr Kee.

The researchers at Leeds are now collaborating with the JPL team to understand how these early batteries and the “chemical life” they were part of may have developed into biological life. They will be building a “geological fuel cell” at the University of Leeds’ Faculty of Engineering — currently used to test new fuel cells — using minerals and gases common on the early Earth. They will apply various chemicals to its surface and monitor the reactions taking place and what chemicals develop.

Another avenue for the team is to travel to Disko Island in Greenland, home to the world’s only naturally occurring source of schreibersite, where they hope to repeat their experiments and show that the same chemicals develop in an entirely Earth-originated setting.